Question

The recipe requires $3\dfrac{1}{4}$ cup of flour. Radha has $1\dfrac{3}{8}$ cup of flour. How many more cups of flour does she need?

Answer 1

Hint: To solve this question, we will first convert all values of mixed fraction to fractions using the formula $a\dfrac{b}{c}=\dfrac{a\times c+b}{b}$. Finally, the cups needed more can be calculated by subtracting total cups with the amount of cups Radha already has.

Complete step by step answer:
The total amount of cup that the recipe need is $3\dfrac{1}{4}$
Let us convert it to fractions first. Converting we have:
\[3\dfrac{1}{4}=\dfrac{4\times 3+1}{4}=\dfrac{12+1}{4}=\dfrac{13}{4}\]
So the recipe requires $\dfrac{13}{4}$ cups of flour.
Radha has $1\dfrac{3}{8}$ cups of flour.
Converting this to fraction we get:
\[1\dfrac{3}{8}=\dfrac{8\times 1+3}{8}=\dfrac{8+3}{8}=\dfrac{11}{8}\]
So, Radha has $\dfrac{11}{8}$ cups of flour.
The amount of flour needed can be calculated by subtracting the amount of cup Radha has from total required cups of flour.
Cups of flour she needs is $\Rightarrow \dfrac{13}{4}-\dfrac{11}{8}$
Taking LCM of above we get:
\[\begin{align}
  & \text{LCM}\left( 4,8 \right)=8 \\
 & \Rightarrow \dfrac{13}{4}-\dfrac{11}{8} \\
 & \Rightarrow \dfrac{13\times 2-11}{8}=\dfrac{26-11}{8} \\
 & \Rightarrow \dfrac{15}{8} \\
\end{align}\]

So, $\dfrac{15}{8}$ cups of flour is needed more to make the recipe.

Note: In this type of questions, always remember to convert mixed fraction to fraction so that addition and subtraction becomes easy.
Also here in the end when $\dfrac{15}{8}$ is obtained as the answer, we can convert it to mixed fraction again as all original values were given as mixed fraction $\dfrac{15}{8}=8\overset{1}{\overline{\left){\begin{align}
  & 15 \\
 & \underline{8} \\
 & 7 \\
\end{align}}\right.}}=1\dfrac{7}{8}$ cups is needed.
Anyway both the answers are correct.